Novel combustion technologies

The novel combustion technologies include advanced burners (MILD combustion), new mode for internal combustion engines (low temperature combustion), and alternative micro gas turbine cycles (micro humid air turbine).

MILD combustion

MILD combustion is a combustion mode able to provide high combustion efficiency with low pollutant emissions, even with very high air preheating, by diluting the reactants with recycled flue gases. The strong recirculation of flue gas into the reaction zone is achieved by the internal aerodynamics of the combustion chamber. This results in a localized reduction of O2 level, leading to a distributed reaction zone and reduced working temperatures with respect to conventional flames. The reduced temperature levels allow reducing the formation of specific classes pollutants (NOx, soot) and it is also very beneficial for the resistance of materials, which are not anymore subject to very sharp temperature gradients. MILD combustion ensures large fuel flexibility, representing an ideal technology for low-calorific value fuels, high-calorific industrial wastes and hydrogen-based fuels.

MILD.001Even though several studies have been devoted to understanding operational conditions of MILD combustion as well as underlying mechanisms and critical parameters, such a combustion regime appears to be still worthy of further investigations and attention, especially for the interactions between turbulent mixing and chemical kinetics. BURN is very active in the development of modelling approaches to account for such overlap between chemical and fluid dynamic time scales, as well as to reduce the chemistry cost in "detailed" kinetic calculations.

More details on our work in MILD combustion can be found here:

[1] Fortunato, V., Galletti, C., Tognotti, L., & Parente, A. (2015). Influence of modelling and scenario uncertainties on the numerical simulation of a semi-industrial flameless furnace. Applied thermal engineering, 76, 324-334.  link
[2] Parente, A., Galetti, C., Tognotti, L., et al. (2012). Experimental and numerical investigation of a micro-CHP flameless unit. Applied energy, 89, 203–214.. link
[3] Parente, A., Sutherland, J., Dally, B., Tognotti, L., & Smith, P. (2011). Investigation of the MILD combustion regime via Principal Component Analysis. Proceedings of the Combustion Institute, 33, 3333-3341.  link

Homogeneous Charge Compression Ignition Engines

In Homogeneous Charge Compression Ignition (HCCI) engines, a premixed homogeneous charge at a particular temperature, pressure and composition is compressed, to the point of autoignition at a preferable position near the TDC. The lack of direct control on the ignition initiation is one of the major challenges of the HCCI engine and the main difference in comparison with the SI and CI engines. The flexibility of the HCCI combustion, and more generally the Low Temperature Combustion (LTC) modes, allows modifying the operating parameters to suit various fuels and conditions. In that context, we operate the HCCI engine using syngas directly from the gasifier without any scrubbing of the tars. We also investigate the use of various non-conventional fuels in LTC.

The following publications give some examples of our work on HCCI:

[1] F. Contino et al., Energ. Fuel, 25(3):998–1003, 2011. link
[2] F. Contino et al., Energ. Fuel, 25(4):1497–1503, 2011. link
[3] S. Bhaduri et al., Energy, Accepted, DOI:10.1016/j.energy.2015.04.076. link
 

Micro Humid Air Turbine 

Micro Gas Turbines (mGTs) have arisen as a promising technology for Combined Heat and Power (CHP) thanks to their overall energy efficiencies of 80% (30% electrical + 50% thermal) and the advantages they offer with respect to internal combustion engines: cleaner exhaust, lower maintenance costs, lower vibration levels, etc. The main limitation of mGTs lies in their rather low electrical efficiency: whenever there is no heat demand, the exhaust gases are directly blown off and the efficiency of the unit is reduced to the electrical component. i.e. 30%. Operation in such conditions is generally not economical and can eventually lead to shutdown of the machine.

Micro Humid Air Turbines (mHATs) are a novel cycle based on micro Gas Turbines (mGTs), where the heat in the exhaust gases—whenever not required for external heating purposes—is used to warm up water which is then injected back into the cycle, at the back of the compressor. The electrical efficiency of the unit improves due to two reasons: first, the mass flow though the turbine augments for a given compressor input and therefore so does the power output of the machine. Second, the heat in the exhaust gases is re-introduced in the cycle through the warm water, further contributing to the increase in electrical efficiency.

At Vrije Universiteit Brussel (VUB) we have constructed a first-of-it’s kind mHAT facility. It is based on a commercial Turbec T100 mGT which has been coupled with an innovative spray saturation tower. Unlike traditional saturation towers, which make use of packing material to humidify the air, the spray saturation tower uses nozzles to spray water over the airflow. Simulations in Aspen Plus have shown that in this unit the electrical efficiency of the cycle with water injection can increase by 4% (absolute) compared to dry operation. 

Ongoing research concerning the mHAT cycle is carried out through Flexi HAT project.

This handout gives an overview of our research and the following publications give some examples of our work with mHATs:

[1] W. De Paepe et al. (2014) New concept of spray saturation tower for micro Humid Air Turbine applications. Applied Energy link
[2] W. De Paepe et al. (2014) Optimal waste heat recovery in micro gas turbine cycles through liquid water injection. Applied Thermal Engineering  link
[3] M. Montero Carrero et al. (2015) Applied Energy  link